1. Field of the Invention
This invention relates to a heat-radiation sheet used to cool heat-generating electronic components, and more particularly to a heat-softening heat-radiation sheet whose quality is capable of changing reversibly from a solid into a paste or liquid with an elevation of temperature of electronic components.
2. Description of the Prior Art
In recent years, CPUs and LSIs such as driver ICs and memories, used in personal computers, digital video disks and cell phones generate a larger amount of heat as they have become required a larger power consumption with an improvement in the degree of integration and an achievement of high-speed operation. This may cause mis-operation of electronic apparatus and equipment or break of electronic components, and hence how to dissipate or radiate their heat has greatly come into question.
In electronic apparatus and equipment and so forth, in order to keep temperatures of electronic components from rising during their use, a heat sink is conventionally used which makes use of a metal sheet having a high thermal conductivity, made of brass or the like. This heat sink conducts the heat generated by the electronic components, and radiates the heat from the surface by means of a difference in temperature from that of the air.
In order to well efficiently transmit the heat generated by the electronic components, the heat sink must be kept in close contact with electronic components. However, because of differences in height of electronic components and common differences ascribable to the manner of assemblage, a heat-conductive sheet having a flexibility or a heat-conductive grease is inserted between the electronic components and the heat sink so that the conduction of heat from the electronic components to the heat sink is materialized via such a heat-conductive sheet or heat-conductive grease. As the heat-conductive sheet, a heat-conducting sheet (e.g., a heat-conductive silicone rubber sheet) formed of heat-conductive silicone rubber is used. As the heat-conductive grease, a heat-conductive silicone grease is used.
However, in heat-conductive silicone rubber sheets conventionally used, contact thermal resistance exists at the interface between the sheet and the electronic components, and hence there is a limit to the performance of heat conduction. This is a great problem for the cooling of CPUs which generate a large amount of heat and are driven at a high frequency. Accordingly, it has been sought to lessen the interfacial contact thermal resistance.
Meanwhile, the heat-conductive silicone grease has a quality close to a liquid, and hence has the interfacial contact thermal resistance at an almost negligible level and has a good performance of heat conduction. It, however, has problems that it requires a device exclusively used therefor, such as a dispenser, and involves a poor operability when collected.